Electronic part

ABSTRACT

An electronic part is provided ( 1 ) containing an electronic element ( 2 ) and a substrate ( 3 ) to which the electronic element ( 2 ) is mounted, the electronic element ( 2 ) and the substrate ( 3 ) being electrically or mechanically connected to each other by means of at least three bumps ( 4 ). Both the value obtained by dividing the total bonding-area of the bumps ( 4 ) bonded to the electronic element ( 2 ) by the mass of the electronic element ( 2 ) and the value obtained by dividing the total bonding-area of the bumps ( 4 ) bonded to the substrate ( 3 ) by the mass of the electronic element ( 2 ) are at least 8.8 mm 2 /g.

TECHNICAL FIELD

[0001] The present invention relates to an electronic part comprising anelectronic element and a substrate on which the electronic element ismounted.

BACKGROUND ART

[0002] In recent years, the sizes and heights of electronic partscomprising electronic elements and substrates on which the electronicelements are mounted have been increasingly reduced. In such situations,a process in which a predetermined surface of an electronic element andthat of a substrate are mechanically or electrically connected to eachother by means of electrically conductive bumps, the so-called flip-chipprocess, is often employed.

[0003]FIGS. 1A and B are respective different longitudinal crosssectional views of an electronic part 10 using a generally-usedflip-chip process of the related art.

[0004] As shown in FIGS. 1A and B, the electronic part 10 comprises anelectronic element 20 and a substrate 30 onto which the electronicelement 20 is mounted.

[0005] As shown in FIG. 1A, a predetermined functional surface 120 ofthe electronic element 20 is positioned so as to face in a particulardirection (downwards in FIG. 1A), and is opposed to a predeterminedmount surface 130 of the substrate 30. The electronic element 20 and thesubstrate 30 are connected to each other electrically and mechanicallyby means of metallic bumps 40 interposed between them. Moreover, asshown in FIG. 1B, to strengthen the connection, a method of filling aresin 90 between the electronic element 20 and the substrate 30 isgenerally known, for example, in the semiconductor device field and soforth. The resin 90 used for the above-described purpose is generallycalled an under-fill.

[0006] However, in the case of electronic parts in which electrodes orthe like are provided on the functional surfaces of electronic elementssuch as surface acoustic wave elements, and the functions of theelements cannot sufficiently be achieved if a resin adheres to thefunctional surfaces, the under-fill cannot be applied. Accordingly, theelectronic elements are mechanically connected to the mount surfaces ofthe substrates by means of the bumps only. If the total contact-area ofthe bumps based on the mass of an electronic element is small, problemswill arise in that the electronic element is released from the bumps,due to external mechanical loads caused by falling, vibration, and thelike, and the functions of the electronic part itself are deteriorated.

DISCLOSURE OF INVENTION

[0007] In view of the foregoing, the present invention has been devised.It is an object of the present invention to provide an electronic partin which an electronic element and a substrate can be mechanicallybonded to each other with sufficient strength.

[0008] To achieve the above-described object, the electronic part of thepresent invention containing an electronic element and a substrate towhich the electronic element is mounted, the electronic element and thesubstrate being electrically or mechanically connected to each other bymeans of at least three bumps, is characterized in that both the valueobtained by dividing the total bonding-area of the bumps bonded to theelectronic element by the mass of the electronic element and the valueobtained by dividing the total bonding-area of the bumps bonded to thesubstrate by the mass of the electronic element are at least 8.8 mm²/g.

[0009] It is advantageous if both the value obtained by dividing thetotal bonding-area of the bumps bonded to the electronic element by themass of the electronic element and the value obtained by dividing thetotal bonding-area of the bumps bonded to the substrate by the mass ofthe electronic element are at least 11.6 mm²/g.

[0010] Moreover, the electronic part of the present invention ispreferably characterized in that the bumps are made of Au or an alloycontaining Au as a major component.

[0011] Furthermore, the electronic part of the present invention ispreferably characterized in that the electronic element and thesubstrate are mechanically connected to each other by means of the bumpsonly.

[0012] Also, in the electronic part of the present invention, theelectronic element may be a surface acoustic wave element comprising atleast one IDT electrode formed on a piezoelectric substrate.

[0013] According to the electronic part of the present invention,mechanical bonding at a sufficient strength can be attained even for asurface acoustic wave device as the electronic part containing a surfaceacoustic wave element in which an under-fill cannot be used for bondingof the electronic element to a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIGS. 1A and B are respective different longitudinalcross-sectional views of an electronic part using a generally-usedflip-chip process of the related art.

[0015]FIG. 2 is a perspective view of an electronic part according to anembodiment of the present invention.

[0016]FIG. 3 is a longitudinal cross-sectional view of the electronicpart of the embodiment of FIG. 2.

[0017]FIG. 4 is a perspective view of a surface acoustic wave element asan example electronic element the functional surface of which ispositioned on the upper side in the figure.

[0018]FIG. 5 is a table showing the relationship between the valueobtained by dividing the total bonding-area of metal bumps by the massof the electronic element and the fault ratio measured by a fallingtest.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will bedescribed with reference to FIGS. 2 to 4.

[0020]FIG. 2 is a perspective view of an electronic part 1 according toan embodiment of the present invention. FIG. 3 is a longitudinalcross-sectional view of the electronic part 1 of this embodiment.Moreover, FIG. 4 is a perspective view of an electronic element 2, whichin this example is a surface acoustic wave element, having a functionalsurface 12 positioned on the upper side thereof when oriented as shownin the figure.

[0021] In this embodiment, the electronic part 1 is a surface mountpart, and is to be mounted onto a mother board (not shown). As shown inFIGS. 2, 3, and 4, the electronic part 1 comprises the electronicelement 2 and a substrate 3. The electronic element 2 is, for example, asurface acoustic wave element having at least one IDT electrode formedon a predetermined functional surface of a piezoelectric substrate. Thesubstrate 3 is made of an insulating material such as a ceramicsmaterial, resins, or the like, and has a predetermined mount surface onwhich the electronic element 2 is mounted. The substrate 3 having theelectronic element 2 mounted thereto is covered with a lid, and theelectronic element 2 is also covered with the lid, though not shown inFIGS. 2, 3, and 4.

[0022] As shown in FIG. 4, in the electronic element 2, which is asurface acoustic wave element, an IDT (interdigital) electrode 21 fortransmitting-receiving a surface acoustic wave and electrode pads 22 areformed on a predetermined functional surface 12 thereof. The IDTelectrode 21 and the electrode pads 22 are formed so that predeterminedelectrical characteristics can be obtained. Metallic bumps 4, e.g., madeof Au or an alloy containing Au as a major component are formed on theelectrode pads 22. In this embodiment, one metallic bump 4 is formed oneach of the four metallic pads 22, as shown in FIG. 4. For formation ofthe metallic bumps, the publicly-known wire-bumping method is employed.

[0023] If the metallic bumps are formed in the total number of one ortwo, a force such as a moment will be readily applied to the electronicpart 1 when mechanical impact, which may be caused by falling or thelike, is added to the electronic part 1. Thus, the durability of theelectronic part 1 to impact will be deteriorated. For this reason, themetallic bumps 4 are preferably formed in the number of at least three.The electrode pads 22 comprise electrically conductive electrodes eachcontaining Al as a major component which are formed on an undercoatelectrode with a contact metal (a thin-film containing as a maincomponent Ti, Ni, NiCr, or the like) being interposed between the padsand the undercoat electrode, the undercoat electrode being formedsimultaneously with the IDT electrode 21 by the publicly-knownphotolithography, though not shown in FIG. 4.

[0024] As shown in FIGS. 2 and 3, internal electrode terminals 31 areprovided on the predetermined mount surface 13 of the substrate 3, andare connected to the metallic bumps 4. Furthermore, external electrodeterminals 32 with which the electronic part 1 can be surface-mountedonto a mother board (not shown) are formed on the side of the substrate3 opposite to the mount surface 13. The internal electrode terminals 31and the external electrode terminals 32 are electrically connected toeach other by means of conductors formed on the side faces of thesubstrate 3. In this embodiment, the internal electrode terminals 31,the external electrode terminals 32, and the conductors connecting theseterminals contain W (wolfram) as a major component, and have Ni and Auplated thereon in this order, respectively.

[0025] The electronic element 2, which in this example is a surfaceacoustic wave element, is connected and fixed to the internal electrodeterminals 31 formed on the mount surface 13 of the substrate 3electrically and mechanically via the metallic bumps 4, e.g., by thepublicly-known flip-chip bonding method using both of supersonic wavesand heat. The surface of the internal electrode terminals 31, which isplated with Au, can be sufficiently bonded to the metallic bumps made ofAu or comprising Au, due to the Au—Au bond. It should be noted that nounder-fill or the like is used, since the electronic element 2 is asurface acoustic wave element.

[0026] In the electronic part 1 described above, both of the valueobtained by dividing the total area in which the metallic bumps 4 andthe electronic element 2 are bonded to each other by the mass of theelectronic element 2 and the value obtained by dividing the total areain which the metallic bumps 4 and the substrate 3 are bonded to eachother by the mass of the electronic element 2 are set at 8.8 mm²/g. Thisis carried out, since no under-fill is used, that is, in order toprevent the mechanical bond between the electronic element 2 and thesubstrate 3 from being deteriorated.

[0027] Hereinafter, a description will be given with reference to FIG.5, of the relationship between the fault ratio of the electronic part 1measured by the falling test, the value obtained by dividing the totalarea in which the metallic bumps 4 and the electronic element 2 arebonded to each other by the mass of the electronic element 2, and thevalue obtained by dividing the total area in which the metallic bumps 4and the substrate 3 are bonded to each other by the mass of theelectronic element 2.

[0028]FIG. 5 is a table showing the relationship between the valueobtained by dividing the total area in which the metallic bumps 4 andthe electronic element 2 are connected to each other by the mass of theelectronic element 2, and the fault ratio measured by the falling test.

[0029] For this falling test, 100 samples each containing as theelectronic element 2 a surface acoustic wave element of LiTaO₃ having aweight of 3.52 mg were prepared and were mounted to the substrate andsubjected to the load-falling test. The fault ratio was measured. Inparticular, the test was conducted assuming that the electronic partwould be used in a portable telephone. A sample was fixed to the upperface (that is, the face opposite to that of the weight which comes intocontact with the ground when it falls) of a 100 g weight, with onesurface out of the six faces of the electronic element 2 to be measuredbeing contacted with the upper face of the weight. The sample was madeto fall 16 times from a height of 1.5 m. This was carried out for eachof the six faces of the electronic element 2 having a substantiallyrectangular parallelepiped shape. In this falling test, the totalbonding-area of the metallic bumps 4 bonded to the substrate 3 waslarger than that of the metallic bumps 4 bonded to the electronicelement 2.

[0030] In this embodiment, the total bonding-area of the metallic bumps4 bonded to the electronic element 2 and that of the metallic bumps 4bonded to the substrate 3 are determined as follows.

[0031] Referring to the total bonding-area of the metallic bumps 4bonded to the electronic element 2, in the flip-chip bonding method, themetallic bumps 4 containing Au as a major component are mechanicallybrought into contact with the electrode pads 22 containing Al as a majorcomponent formed on the electronic element 2, and supersonic waves orheat is applied to cause the Au and the Al to diffuse into each other,so that an alloy layer of Au and Al is formed. The alloy layercontributes to the bonding. Thus, the bonding-area of the alloy layer istaken as the total bonding-area. To determine the total bonding-area,the electronic part 1 of the present invention is dipped intohydrochloric acid to dissolve the electrode pads 22 containing Al as amajor component. Thus, the metallic bumps 4 containing Au as a majorcomponent are separated from the electronic element 2. Observation ofthe surface of the metallic bumps 4 shows that the Au is gold in color,while the alloy layer comprising Au and Al is gray. The area of theportion of the surface of each metallic bump 4 which contacted theelectrode pad 22 before the separation, and on which the alloy layer ofAl and Au is formed, is measured. The total of the areas is taken as thetotal bonding-area of the metallic bumps 4 bonded to the electronicelement 2. The area of the portion of the metallic bump 4 on which thealloy layer of Al and Au is formed is measured by means of a microscopewith which calculation can be carried out.

[0032] Referring to the total bonding-area of the metallic bumps 4bonded to the substrate 3, the bonding-surface of the substrate isplated with Au, and the metallic bumps 4 contain Au as a majorcomponent. Thus, the substrate 3 and the metallic bumps 4 are bonded toeach other by means of the same type materials. Accordingly, the contactarea of each bump 4 is measured, and the total area is taken as thetotal-bonding area of the metallic bumps 4 bonded to the substrate 3.The contact-area of each bump 4 is measured by a red-check method or thelike. According to the red-check method, an electronic part is dippedinto red ink, so that the surface of the electronic part is colored red.Thereafter, a metallic bump is separated from the substrate, and thearea of the portion of the substrate not colored red is measured.

[0033] As shown in FIG. 5, the fault ratio of the electronic part 1obtained by the falling test was 31% for a value of 6.000 mm²/g obtainedby dividing the total bonding-area of the metallic bumps 4 bonded to theelectronic element 2 by the mass of the electronic element 2.

[0034] Moreover, the fault ratio of the electronic part 1 obtained bythe falling test was 15% for a value of 8.000 mm²/g obtained by dividingthe total bonding-area. of the metallic bumps 4 bonded to the electronicelement 2 by the mass of the electronic element 2.

[0035] On the other hand, the fault ratio of the electronic part 1obtained by the falling test was low, that is, 7% for a value of 8.800mm²/g obtained by dividing the total bonding-area of the metallic bumps4 bonded to the electronic element 2 by the mass of the electronicelement 2.

[0036] For this value of 8.800 mm²/g, there are very few cases in whicha portable telephone, as an example, fails when it falls less than 100times, due to the carelessness of a user. Thus, when the fault ratio isreduced to 7%, it may be concluded that the durability of the electronicpart 1 has substantially no problems in its practical use.

[0037] Accordingly, it is preferable that the value obtained by dividingthe total bonding-area of the metallic bumps 4 bonded to the electronicelement 2 by the mass of the electronic element 2 is set at 8.8 mm²/g orhigher. Thus, high quality electronic parts are provided having faultratios, which may be caused by falling, that are low. More preferably,the value obtained by dividing the total bonding-area of the metallicbumps 4 bonded to the electronic element 2 is set at 11.6 mm²/g orhigher. In this case, the falling test shows a fault ratio of 0%. Inpractice, the fault, which may be caused by falling, can be preventedsubstantially perfectly.

[0038] It should be noted that this falling test deals with the case inwhich the total contact-area of the metallic bumps 4 contacting thesubstrate 3 is larger than the total bonding-area of the metallic bumps4 bonded to the electronic element 2. Similar results are obtained inthe case in which the total bonding-area of the metallic bumps 4 bondedto the electronic element 2 is larger than the total contact-area of themetallic bumps 4 contacting the substrate 3.

[0039] Although the above description gives details of the preferredstructure and properties of the electronic part according to oneembodiment of the invention, it is to be understood that the presentinvention is not limited by the particularities mentioned therein. Moreparticularly, numerous modifications and variations can be made.

[0040] For example, in this embodiment, the metallic bumps 4 are formedby a wire-bumping method. This method is not restrictive. The metallicbumps 4 may be formed, e.g., by a plating method.

[0041] Moreover, in this embodiment, as an example of the structure ofthe electrode pads 22, the conductive material containing Al as a majorcomponent and the contact metal are laminated. The lamination is notrestrictive. The electrode pads 22 may be formed simultaneously with theIDT electrode 21 by a photolithography. The number of layers can bedesirably selected. Moreover, the configurations of the IDT electrode 21and the electrode pads 22 are not limited to those shown in FIG. 4.

[0042] In this embodiment, the internal electrode terminals 31, theexternal electrode terminals 32, and the conductors connecting theseelectrodes each have a structure in which Ni and Au are plated onto W(wolfram). This is not restrictive. It is preferred that the uppermostlayer is made of Au for its sufficient connection to the metallic bumps4 made of Au or an alloy containing Au as a major component.

[0043] Also, in this embodiment, the flip-chip bonding method employsboth supersonic waves and heat. Flip-chip bonding using either heat orsupersonic waves can be applied without any trouble.

[0044] Furthermore, in this embodiment of the present invention, as theelectronic part 1, a surface mount part mounted on a mother board isemployed as an example. This is not restrictive. Needless to say, thepresent invention may be applied to an electronic part (not shown)comprising an electronic element mounted directly onto a mother board.

[0045] Industrial Applicability

[0046] According to the electronic part of the present invention, boththe value obtained by dividing the total bonding-area of the pluralbumps bonded to the electronic element by the mass of the electronicelement and the value obtained by dividing the total contact-area of thebumps contacting the substrate by the mass of the electronic element areset at 8.8 mm²/g or higher, or preferably 11.6 mm²/g or higher. Thus,mechanical bonding at a sufficient strength can be attained even forelectronic parts such as surface acoustic wave devices each containing asurface acoustic wave element in which an under-fill can not be used forbonding of the electronic element to a substrate.

1. An electronic part (1) containing an electronic element (2) and asubstrate (3) to which the electronic element (2) is mounted, theelectronic element (2) and the substrate (3) being electrically ormechanically connected to each other by means of at least three bumps(4), characterized in that both the value obtained by dividing the totalbonding-area of the bumps (4) bonded to the electronic element (2) bythe mass of the electronic element (2) and the value obtained bydividing the total bonding-area of the bumps (4) bonded to the substrate(3) by the mass of the electronic element (2) are at least 8.8 mm²/g. 2.An electronic part according to claim 1, wherein both the value obtainedby dividing the total bonding-area of the bumps (4) bonded to theelectronic element (2) by the mass of the electronic element (2) and thevalue obtained by dividing the total bonding-area of the bumps (4)bonded to the substrate (3) by the mass of the electronic element (2)are at least 11.6 mm²/g.
 3. An electronic part according to one ofclaims 1 and 2, characterized in that the electronic element (2) and thesubstrate (3) are mechanically connected to each other by means of thebumps (4) only.
 4. An electronic part (1) according to any one of claim1, characterized in that the bumps (4) are made of Au or an alloycontaining Au as a major component.
 5. An electronic part (1) accordingto any one of claim 1, characterized in that the electronic element (2)is a surface acoustic wave element comprising at least one IDT electrode(21) formed on a piezoelectric substrate.